In One Piece, few groups are as iconic as the Monster Trio of the Straw Hats. Made up of Luffy, Zoro and Sanji, the three represent the true strength and power of this burgeoning pirate crew. However, in the case of Sanji, his role as a member of this unofficial team has somewhat been jeopardized as of late. Recently though, during the raid of Onigashima, Sanji has been given a massive power boost that could change this.
The raid of Onigashima has created multiple reasons for fans to believe Sanji won't (or more accurately, can't) remain part of the Monster Trio due to no longer being the third-strongest crew member. With the arrival of Jimbe and the possibility of Yamato joining the Straw Hats, it's easy to see why fans were starting to doubt his abilities. With far fewer victories under his belt since the time skip, Sanji just hasn't been given many moments to shine. Even Whole Cake Island, an arc dedicated to him, did more to develop and explain his character rather than power him up in any way.
However, now that his Germa 66 enhancements have seemingly awakened, Sanji might have the power to put all these doubts to rest. With enhanced strength and a super durable exoskeleton responsible for his siblings' famous "iron bodies," Sanji's physical abilities are now on a whole new level. To top it off, he even has a healing factor, which seemingly allows him to repair any broken bones instantly and other wounds exponentially faster than a normal human.
There's also the question of his unique ability. While it isn't confirmed that he has access to one, his four other siblings each have a power unique to them. Reiju has her "Poison Pink" powers, Ichiji has his "Sparking Red," Niji has his "Electric Shock Blue" and Yonji has his "Winch Green," so it's quite possible that Sanji also has his own. Most likely, it will have something to do with the name "Stealth Black" -- his character's name in the fictional comic starring Germa 66 -- as his Raid Suit is the same as it is in the comic. It's also possible that it is his Diable Jambe technique, as even Queen was confused by how he was able to use it.
Speaking of the Raid Suit, this has already proven to be an incredible tool for Sanji to put to use, as it further increases his physical abilities as well as giving him the ability to fly. Sanji becomes a much bigger threat to his enemies than he would be without it, and it even has its own unique ability -- being able to turn itself invisible whenever the user chooses (unfortunately helping to fulfill Sanji's dream of being able to peek on women without their knowledge).
While not directly stated, it can be assumed that the Raid Suit's physical enhancements aren't necessarily set in stone. That is to say, the boost to his strength isn't going to be the same now as it was before the suit awakened his Germa 66 enhancements. Rather, it will likely increase whatever his base strength is by the same amount as it did before. This would effectively mean that if Sanji's strength were to increase on its own without any equipment, then with the suit, Sanji's power would increase even further, most likely in proportion to the growth his body experienced.
That being said, it's still unknown how Sanji's awakened body will react to the Raid Suit now, as well as if/how it will affect the suit's abilities going forward. All that can be clearly ascertained is that even without using it or any Armament Haki, Sanji's body is durable enough that his skull was able to shatter Queen's sword with little to no damage. Sanji himself barely seemed to notice the attack, highlighting just how much stronger he's become.
With all these new upgrades, it's easy to forget that Sanji is also a practitioner of Haki. As the foremost power to be used in the New World, with its effectiveness arguably higher than that of a Devil Fruit, it would make sense for Sanji to be capable of using it. Currently able to use both Armament and Observation Haki, with more of an affinity for the latter (enough that he can access the advanced Future Sight ability), Sanji's combat potential received a huge boost thanks to his enhancements.
Already before his body's awakening, Sanji's physical abilities and Haki were great enough that he was able to overpower his brother Yonji and prove stronger than even his father (who only won their match by "cheating"). Now though, he can approach combat in a way similar to Luffy, in that he can combine his Haki with his body's unique abilities. By merging the two, he can achieve a power greater than neither he nor his family members ever had before.
While all these new abilities help cement Sanji as one of the wings of the Pirate King, it also helps bridge the once ever-growing gap between himself and Zoro. Since the Alabasta Saga, Zoro and Sanji's rivalry has remained a fixture within the crew dynamic, with many of their moments together highlighting it. Unfortunately, as the series went on, it became increasingly noticeable that Zoro was at a higher level.
At a certain point, the strength rankings became such that Sanji was either at Zoro's level or slightly weaker, Zoro was either at Luffy's level or slightly weaker and Luffy was the pinnacle of the crew's strength. While Zoro's exact strength wasn't clear, it was obvious that Sanji was being written as the weakest of the three. This was further illustrated when only Zoro joined Luffy against Kaido and their subsequent unlocking of Advanced Conqueror's Haki. While that was meant to be a fight between the Yonko and Worst Generation, it also highlights how Sanji was unable to qualify for that unofficial group even after Enies Lobby like Zoro did.
Now though, all this has suddenly changed. Sanji's body is currently arguably the most durable of the crew's, even more so than Luffy's and definitely more than Zoro's. On top of that, his new power comes at seemingly no cost to himself and is always active, as opposed to Haki-based powers and swordsmanship techniques. In this way, Sanji is able to stand comfortably among the rest of the Monster Trio in a way he previously couldn't.
At the moment, the only thing that sets him apart from his captain and rival is his lack of Conqueror's Haki. As possibly the greatest power in One Piece, with only the strongest beings able to use it, Sanji is in a curious position.
Being the son of a king as well as someone hoping to become the best there is at what he does (much like Luffy wanting to be the Pirate King and Zoro wanting to be the world's greatest swordsman), Sanji meets many of the requirements for having Conqueror's Haki. Unfortunately, so much is unknown about it that it's impossible to accurately guess who has it and who doesn't -- however, it's possible that Sanji has it without realizing it, much as Zoro did.
In short, Sanji is currently one of the strongest members of the Straw Hats as well as one of the strongest beings in the New World. As of now, Sanji should be able to match someone such as Zoro, especially if he were to use his Raid Suit. With all his new abilities combined with his old ones, he can now fulfill his duty of supporting Luffy until and after the latter becomes the King of Pirates.
